218 FLORA INDTCA.
and are hence gradually drying up. This diminution of many
of the lakes is 'no doubt entirely attributable to a change of
climate, which is extremely interesting in a botanical point of
view, from its favouring the immigration of many saline types
of the Caspian flora.
Where the surface is covered with salt-marshes, are found
Glaux maritima, Eurotia, Corispermum, Caroxylon, Su&da,
Salsola, Chenopodium, Ambrina, Christolea^ Triglochin; and a
large Nostoc, of a species eaten in China, floats on the surface
of the pools. The carbonate of soda again appears to have
no appreciable effect on the vegetation of the dry soil it en-
crusts; grasses, tufted Androsace?, Astragali) Gnaphalia, Ar-
temisia, etc., being alike covered with it.
Cultivation in Tibet attains the height of 15,000 feet, and
is luxuriant below 12,000 feet, barley and wheat being the
grains cultivated, with rape and millet at lower levels. The
indigenous vegetation is everywhere scanty. Though there is
no forest, the banks of the rivers and streams are skirted by
a dense scrub of bushes, chiefly Myricaria, Hippophae, Rosa,
m&Lonicera. Populus balsamifera and Euphratici, and Juni-
perus excelsa are the only trees, and these occur rarely; as
does Pinus excelsa^ which is only found towards the confines
of Hasora, and can hardly be considered a Tibetan tree. My~
ricaria and Hippophae occasionally attain a height of twenty
feet. Of cultivated trees, apricots and Populus balsamifera are
seen up to 12,000 feet; apples, walnut, the black poplar, and
Elaagnus up to 11,000 feet, pears to 10,000 feet, and grapes
and white poplar and plane-trees to 9000 feet.
Subtropical types ascend along the course'of the Indus
to Bondu and Iskardo, and some of them even as far as 11,000
feet, in Nubra and lie, of which the following genera arc ex-
Peganum. Tamarix GMica.